Studio tone control



March 14, 1950 P. F. G. HOLST 2,500,493

s'rumo TONE CONTROL Filed Feb. 19, 1949 Patented Mar. 14, 1950 UNITED STATES at ases ,rr OFFICE STUDIO TONE CONTRUL Application February 19, 1949, Serial No. 77,309

"1 Claims.

The present invention relates to tone controls and more particularly to a wide range tone control particularly suited for radio receivers for producing certain compensating effects at different audio sound levels.

It is well known that a great difierence exists between the audio sound level of a person speaking in a broadcasting studio and the audio sound level of a symphony orchestra. The level of transmission as indicated by the depth of modulation radiated by the broadcasting station, however, does not correspondingly vary. It or course is known that the radio station erators ride the gain control so that the transmitted variations in sound level are kept within a certain range. Quite obviously no compensation is provided for at the radio receiver. duction usually is at a sound level quite different from the level of sound from the original source. According to the authority Fletcher a change of the sound level of the reproduced sound when compared with the original or normal level of sound from the source produces on the listener an effect of an apparent change in tonal characteristic.

It of course has been observed by many individuals having radio receivers that when itis desired to set the volume level at a particular value it sometimes is necessary to adjust the tone control in order to make the reproduction more pleasing and natural. The tone control provided in the average radio receiver, however, is incapable of providing sufficient compensation to overcome the apparent change in tonal characteristic referred to by Fletcher.

It, therefore, is apparent that it would be desirable to provide an improved tone control having a relatively wide range which could be adjusted so as to provide the desired compensation for any volume level of reproduction so that the tonal characteristic would more nearly correspond to the tonal characteristic of the sound from the original source.

It, therefore, is an object of the present invention to provide an improved wide range tone control for sound reproducing circuits.

Another object of the present invention is to provide a wide range tone control which maintains the output level constant independent of the volume control setting.

Still another object of the present invention is to provide a tone control for compensating at the receiver for variations in broadcasting. studio audio sound level.

Still another object of the present invention is Thus the reproto provide in a wide range tone control an additional control of the high audio frequency range independent of the adjustable or variable tone control.

Other and further objects of the present invention subsequently will become apparent by reference to the following description taken in conjunction with the accompanying drawings wherein:

Fig. l is a circuit diagram of one embodiment of the present invention;

Fig. 2 is a graphical representation of the approximate characteristics obtained at certain points in the circuit of Fig. 1;

Fig. Sis another graphical representation of the approximate characteristics obtained at certain other points in the circuit of Fig. 1;

Fig. l is a circuit diagram of another embodiment of the present invention;

Fig. 5 is a graphical representation of certain characteristics obtained by the circuit of Fig. 4; and

Fig. 6 is a graphical representation illustrating certain other characteristics of the operation of the circuit of Fig. 4.

Referring to Fig. 1 of the drawing there is shown a vacuum tube I! having a cathode bias resistor l2 and a bypass capacitor l3. This representation of a tube II is intended to denote the first stage of an audio frequency amplifier. The present invention consists of a circuit interposed between the first audio frequency amplifier and the audio input thereto which in a radio receiver is obtained from the detector tube. While it has been mentioned that the present invention is particularly suited for producing certain compensating efiects because of the difference in transmission of the levels of sound from a radio station, it of course will be appreciated that the circuit likewise may be used for compensation in the reproduction of phonograph records particularly where such records are to be reproduced at certain desired sound levels.

The grid of the first audio amplifier tube H is connected to the adjustable contact [4 of a variable resistor 15 which is of the potentiometer type. One terminal of the resistor 15 is connected to an adjustable contact I6 of a resistor H. The other terminal of the resistor i5 is connected to another adjustable or movable contact l8 of a resistor l9.

The resistor ii is connected between ground and the input conductor 2| through a coupling capacitor 22. At an intermediate point on the resistor H a tap is provided for the connection of a capacitor 23 which in turn is connected to ground.

At a point intermediate the grounded terminal of the resistor ill and the point at which the capacitor 23 was connected to the resistor there is provided another tap which is connected to a capacitor 25 which is connected through the resistor 2% to ground. The circuit including a relatively large capacitor 22, the resistor ll, the capacitors and 25 and the resistor 25 is designed to be predominantly responsive to the low frequencies of the audio frequency range. This circuit may be so designed that the response characteristic thereof is satisfactory for the reception and reproduction of a symphony orchestra or it may be so designed that the low fre quency response obtained is slightly greater than that which would normally be required.

The other circuit which includes the resistor I9 connected between ground and the conductor 21 by means of a capacitor 2? is designed to be predominantly responsive to the higher frequencies of the audio frequency range. The resistor is at an intermediate point is also provided with a tap 3' 3 which i's' connected through a resistor 23 to ground. The resistor '28 is also connected to a capacitor as which in turn is connected to the conductor '23. At a point intermediate the first mentioned tap on the resistor is and ground there is provided a second tap which is connected to a capacitor 3! which in turn is connected through a resistor 32 to ground. This combination of a capacitor and resistor serves the same purpose as the capacitor25 and resistor Zi'connect'e'd to the low frequency resistor ll.

This high frequency circuit may be so arranged as to provide adequate high fre'd'uehcy response or even an over-emphasis of the higher frequencies. The low frequency response of the high frequency circuit may be'so arranged as to be satisfactory for the reproduction of speech.

It now will become apparent to those skilled in theart' that the first control which includes the resistor l'i is supplied from the audio frequency input conductor 2! by a relatively large capacitor so as to insure a good low frequency response acrossthe entire resistor ii. The intermediate tap point on the resistor i'iis'loaded with 9. ca-'- pac' itor or with the combination of a resistor and capacitor in series so that the impedance of v this branch is designed to be low compared to the impedance of the control resistor ii. The response of the control circuit at the first tap point will be substantially'the same as the frequency response characteristic of the impedance of the shunting network represented by the ca pacitor 1232 Since this impedance has been selected 'so'as to be high at the low frequency, the low frequency response of the circuit obtained when the adjustable contact is in the proximity of thei'irst mentioned tap willbe one which is relatively high. p

The second shunting network represented by the capacitor 25 and theresistc'r '26serves to further increase-the low frequency response at still lower levels of reproduction.

In the second control which includes the" res'is'tor it th'e coup-ling capacitor Zlis relatively small-so as-to attenuate the low frequencyir'e spcnse. The bypass capacitor is which is in shunt to the upper portion of the resistor 49 bypasses the high frequencies thereby creating a itioh here higlrfrequencies areprominent attire-first tap: Since the first tap-is loadedby the resistor 2%. n acc ehtu'atic n-of any" W" fre 4 quencies occurs there. The second tap point on the resistor is which includes the capacitor 3! and the resistor 32 as a shunt circuit, is provided for the lower levels of reproduction.

By adjusting the contact i6 and i8 simultaneously a change in the volume level is obtained. A

change in the accentuation of the higher ire quencies or lower frequencies is obtained by adjusting the position of the'contact It on the resistor l5.

Thus it will be seen that I have provided, for use in combination with a source of audio frequency signals, a novel studio tone control which comprises a' parallel pair of potentiometers (22, H and 2?, 19) connected across the terminals (2!, ground) of said source, each of said potentiometers having a sliding connection terminal (86 or it) between its end terminals, one of said potentiometers (22, ll) having impedance characteristics which favor'the low frequency components of the audio frequency signals and discriminate against the high frequency compo nents, the other of said potentiometers' (2?, it) having impedance characteristics which'iavor the high frequency components and discriminate against the low frequency components, a third potentiometer comprising a sliding connection terminal is and a resistor i5 connected between the sliding connection terminals (it, it) of said first and second potentiometers. This tone control is shown in association with an amplifier stage it which has an input (grid-cathode) circuit connected to the output circuit formed by the sliding connection terminals M of the third potentiometer and the low potential terminal (ground) of the source. The third slide connec- 'tion terminal H1 is adjustable to vary the relative intensities of the high and low frequency components of the signals appliedto the amplifier stage H. The first it and second to sliding connection terminals are adjustable in unison to vary the level of said signals. A series resistor-capacitor bass boost network (26; is-connecte'd between the lower potential tap on potentiometer i7 and the low potentialend terminal (ground). A series resistor-capacitor bass boost network (3i, 32) is connected between the lower potential tap on potentiometer I 9 and its low potential end terminal (ground). A series treble boost network comprising capacitor 29 and resistor 28 is also provided. It comprises a capacitor which is connested between the high potential tap on poten: tiometer i9 and the high potential end terminal of the potentiometer circuit (21, Hi). It also comprises a resistor 28' connected between the tap 3 d and the low potential end terminal (ground).

Referring to Fig. 2 there is shown in graphical representation the approi'rimate characteristic to be expected at various taps on the resistors i? and if). The curve 33 shows the response to be obtained atthe'first tap on the resistor ll. Curve 34 shows the response at the first tap on resistor 59. The representation 'inFig. 2 illustrates the percentage of response as compared to the fre quency as expressed in cycles per second.

Fig. 3' shows an approximate characteristic curve 35 indicating the response to be obtained at the top of the resistor H. In a similar manner the curve 36 indicates the response'to'beobtained at the top of the resistor 19;

In order to further assist those skilled in the art typical values for-the components employed in Fig. 1 in one installation will be enumerated. The resistors I i and l Q 'aretcui megohm resistors tapped at one and two megohms from the lower extremity. The resistor I5 is a two megohm variable resistor. The resistors I1 and I9 are contained in a dual volume control resistor. The resistors 26, 28 and 32 are each 100,000 ohms.

The coupling capacitor 22 is 5,000 mmf., and the coupling capacitor 21 is 560 mmf. The capacitors 25 and 3| are each 3300 mmf. The circuit loading capacitor 23 is 2500 mmf. The bypass capacitor 29 is 32 mmf. As has been previously stated the circuit shown in Fig. i may have selected characteristics and hence the values given for the different components are not to be considered limitations but merely an explanation of the values encountered in a typical embodiment.

While the circuit illustrated in Fig. 1 has been found entirely satisfactory there are certain times when it would be desirable to have some kind of high frequency control which is independent of the action of the control illustrated in the c rcuit of Fig. 1. Such an arrangement is particularly useful where two different types of operation are desired as in the one instance a maximum low frequency response with additional high frequency response and in the other instance a maximum high frequency response with a less extreme high frequency response. It will be noted that similar reference characters have been appled to similar components in Fig. 4 and that only minor changes have been made. It will be noted that the tap on the resistor i l is connected through a resistor 31 to a capacitor 30. The resistor 31 in this instance had a value of 60,000 ohms and the capacitor had a value of 2700 mmf.

The anode of the first audio vacuum tube II has the usual coupling capacitor 39 and anode resistor 4|. Interposed between the anode and these elements is a connection to a capacitor 42 which is connected to one switch contact of an electrical switch 43 having its contact arm connected to ground.

The change in the shunt circuit connected to the first tap on resistor I! changed the response characteristic from the curve 44 in Fig. 5 to curve 45. The provision of the capacitor 42 and the selector switch 43 at the anode of the vacuum tube H provides a selection between curves 46 and 41 of Fig. 5. Thus it will be appreciated that the switch 43 may be used to provide a greater or lesser amount of the higher audio frequencies without adjustment of the movable contact i4.

While for the purpose of illustrating and describing the present invention certain preferred circuit arrangements have been disclosed in the drawings, it is to be understood that the invention is not to be limited thereby since such variations in the circuit and in the components employed are contemplated as may be commensurate with the spirit and scope of the invention as defined in the accompanying claims.

What I desire to protect by United States Letter Patent is claimed as follows:

1. The combination of a source of audio frequency signals having high frequency and low frequency components, a parallel pair of potentiometers connected across the terminals of said source, each of said potentiometers consisting of a capacitor connected to the high-potential source terminal and a resistor connected between the capacitor and the low-potential source terminal, and each of said potentiometers having an adjustable connection terminal contacting its resistor between its end terminals, one of said Dotentiometers having impedance characteristics Lil which favor said low frequency components and discriminate against said high frequency components, the other of said potentiometers having impedance characteristics which favor said high frequency components and discriminate against said low frequency components, a third potentiometer comprising an adjustable connection terminal and a resistor connected between the adjustable connection terminals of said first and second potentiometers, and an amplifier stage having an input circuit connected to the output circuit formed by the adjustable connection terminal of the third potentiometer and the low potential terminal of said source, the third adjustable connection terminal being positioned to vary the relative intensities of the high and low frequency components of the signals applied to said amplifier stage, the first and second adjustable connection terminals being positioned in unison to vary the level of said signals.

2. The combination of a source of audio fre quency signals having high frequency and low frequency components, a parallel pair of potentiometers connected across the terminals of said source, each of said potentiometers having a sliding connection terminal between its end terminals, said potentiometers having different frequency-response characteristics, a third potentiometer comprising a sliding connection terminal and a resistor connected between the sliding connection terminals of said first and second potentiometers, and an amplifier stage having an input circuit connected to the output circuit formed by the sliding connection terminal of the third potentiometer and the low potential terminal of said source, the third sliding connection terminal being adjustable to vary the relative intensities of the high and low frequency components of the signals applied. to said amplifier stage, the first and second sliding connection terminals being adjustable in unison to vary the level of said signals.

3. The combination of a parallel pair of potentiometers connected across common input terminals, each of said potentiometers having a sliding connection terminal between its end terminals, one of said potentiometers having such impedance characteristics that it favors the low frequency components of an audio signal applied to said input terminals and discriminates against the high frequency components, the other of said potentiometers having such impedance characteristics that it favors said high frequency components and discriminates against said low frequency components, and a third potentiometer comprising a sliding connection terminal and a resistor connected between the sliding connection terminals of said first and second potentiometers, an output circuit being formed by the sliding connection terminal of the third potentiometer and the low potential input terminal, the third sliding connection terminal being adjustable to vary the relative intensities of the high and low frequency components of the signals appearing in said output circuit, the first and second sliding connection terminals being adjustable in unison to vary the level of said signals.

4. The combination of a parallel pair of potentiometers connected across common input terminals, each of said potentiometers having a tap and a sliding connection terminal between its end terminals, one of said potentiometers having such impedance characteristics that it favors the low frequency components of an audio signal applied to said input terminals and discriminates '2 against the high frequency components, the other of said potentiometers having such impedance characteristics that it favors said high frequency components and discriminates against said low frequency components, a third potentiometer comprising a sliding connection terminal and a resistor connected between the sliding connection terminals of said first and second potentiometers, an output circuit being formed by the sliding connection terminal of the third potentiometer and the low potential input terminal, the third sliding connection terminal being adjustable to vary the relative intensities of the high and low frequency components of the signals appearing in said output circuit, the first and second sliding connection terminals being adjustable in unison to vary the level of said signals, and a pair ofseries resistor-capacitor bass boost networks individually connected between each tap and the low potential end terminal of the associated potentiometer.

5. The combination of a parallel pair of potentiometers connected across common input terminals, each of said potentiometers having a pair of taps and a sliding connection terminal between its end terminals, one of said potentiometers having such impedance characteristics that it favors the low frequency components of an audio signal applied to said input terminalsand discriminates against the high frequency components, the other of said potentiometers having such impedance characteristics that it favors said high frequency components and discriminates against said low frequency components, a third potentiometer comprising a sliding connection terminal and a resistor connected between the sliding connection terminals of said first and second potentiometers, an output circuit being formed by the sliding connection terminal of the third potentiometer and the low potential input terminal, the third sliding connection terminal being adjustable to vary the relative intensities of the hi h and low frequency components of the signals appearing in said output circuit, the first and second sliding connection terminals being adjustable inunison to vary the level of said signals, three series resistor-capacitor bass boost networks, two of which are individually connected between each tap ontsaid one potentiometer and its low-potential end terminal, the remaining network being connected between the low-potential end terminal of said other potentiometer and its nearertap.

6. The combination of a parallel pair of potentiometers connected across common input termi! nals, each of said potentiometers having a sliding connection terminal between its end terminals, one of said potentiometers having such'impedance characteristics that it favors the low frequency components of an audio signal applied to said input terminals and discriminates against the high frequency components, the other of said potentiometers having such impedance charac-.- teristics that it favors said high frequency com-. ponents and discriminates against said low frequency components, a third potentiometer comprising a sliding connection terminal and a resistor connected between the sliding connection terminals of said first and second potentiometers, an output circuit being formed by the sliding connection terminal of the third potentiometer and the low potential input terminal, the third sliding connection terminal being adjustable to vary the relative intensitiesof the high and low frequency components of the'signals appearing in said output circuit, the first and second sliding connece tion terminals being adjustable in unison to vary the level of said signals, three series resistor-capacitor bass boost networks, two of which are individually connected between each tap on said one potentiometer and its low-potential end terminal, the remaining network being connected between the low-potential end terminal of said other potentiometer and its nearer tap, and a series treble boost network comprisin a oapacitor between the remaining tap and end terminal of said other potentiometer and a resistor between said remaining tap and its low-potential end terminal.

7. The combination in accordance with claim 6 and means including a series combination of switch and capacitor selectively effectively coupled in shunt with said output circuit to discriminate against the high-frequency components of said signals.

PAUL F. G. I-IOLST.

REFERENCES CITED FOREIGN PATENTS Country Date Australia Apr. 18, 1939 Number 

